# CLAUDE.md — Agent Instructions

This file is read automatically by Claude Code at the start of every session.
Keep it concise — the agent needs signal, not essays.

---

## Project overview

Go 1.24 template / PoC starter. Demonstrates: structured logging (zap),
config (viper), interfaces + mocks (mockery), linting (golangci-lint),
security scanning (gosec, govulncheck), git hooks, devcontainer, VSCode tasks.

Module: `github.com/your-org/go-template` — update this when you fork.

---

## Project structure

```
cmd/app/main.go          composition root — wires deps, no logic here
internal/config/         Viper config loader (config.Load)
internal/logger/         Zap wrapper with WithField / WithFields
internal/greeter/        Example domain package (delete or repurpose)
mocks/greeter/           Generated mocks — regenerate with `make mocks`
config/dev.yaml          Local dev config (committed, no secrets)
tools.go                 Tool version pinning (build tag: tools)
.golangci.yml            Linter rules
.mockery.yaml            Mockery code-gen config
.githooks/pre-commit     Runs gofmt + golangci-lint + gosec before commit
```

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## Project rules

- **Module imports** — always use the full module path `github.com/your-org/go-template/...`
- **Packages** — keep `cmd/` thin (wiring only); business logic belongs in `internal/`
- **Interfaces** — define interfaces where they are *used*, not where they are *implemented*
- **Errors** — wrap with `fmt.Errorf("context: %w", err)`; never swallow errors silently
- **Logging** — use `log.WithField("key", val)` for structured context, never `fmt.Sprintf` in log messages
- **Config** — all configuration through `internal/config`; no hard-coded values in logic packages
- **Secrets** — never commit `.env` files or credentials; use env var overrides of config keys

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## Code style

- Follow `gofmt` + `goimports` formatting (enforced by linter and git hook)
- Imports: stdlib → blank line → external → blank line → internal (goimports handles this)
- Error variables: `err` for local, `ErrFoo` for package-level sentinels
- Constructors: `New(deps...) *Type` pattern
- Comment every exported symbol (golangci-lint will warn if missing)
- Max line length: 120 chars (configured in `.golangci.yml`)
- Prefer explicit over clever; PoC code should be readable first

---

## Testing rules

- All tests use **testify** (`assert` for soft checks, `require` for stop-on-fail)
- Test files: `package foo_test` (black-box) unless white-box access is needed
- Mock dependencies via **mockery**-generated mocks with `EXPECT()` chains
- Use `logger.NewNop()` when the test doesn't care about log output
- Table-driven tests with `t.Run("description", ...)` for multiple cases
- The race detector is enabled in CI (`make test-race`); don't introduce data races
- Never use `time.Sleep` in tests; use channels or `require.Eventually`

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## Development commands

```bash
make init          # first-time setup: fetch deps, install tools, git hooks
make build         # compile to ./bin/app
make run           # go run with config/dev.yaml
make test          # run all tests
make test-race     # tests + race detector
make lint          # golangci-lint
make lint-fix      # auto-fix lint issues
make security      # gosec + govulncheck
make mocks         # regenerate all mocks
make generate      # run all //go:generate directives
make clean         # remove bin/ and mocks/
```

VSCode: `Ctrl+Shift+B` = build, `Ctrl+Shift+T` = test.
Debug: use launch config "Debug: app" (F5).

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## Adding new features (checklist)

1. Define the interface in `internal/<domain>/`
2. Write the implementation and its unit tests
3. Add the interface to `.mockery.yaml` and run `make mocks`
4. Wire it in `cmd/app/main.go`
5. Run `make lint test` before committing

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## Known pitfalls

- `mocks/` are committed intentionally — regenerate after interface changes
- `govulncheck` makes network calls; excluded from pre-commit hook (run manually)
- `config/dev.yaml` is committed but never add real credentials here
- `tools.go` has `//go:build tools` — it won't compile into the binary

---

## Recent work
<!-- Agent: append a dated bullet when completing a significant chunk of work.
     Keep this section to ~10 entries; remove stale items.
     Format: YYYY-MM-DD — what was done and why. -->

- 2026-03-05 — Initial template scaffolded: config, logger, greeter example,
  mocks, git hooks, devcontainer, VSCode tasks, golangci-lint, Makefile.